Consciousness, he says, ‘is the name of a nonentity, and has no right to a place among first principles. Those who still cling to it are clinging to a mere echo, the faint rumour left behind by the disappearing “soul” upon the air of philosophy’. … He holds that there is ‘only one primal stuff or material’, out of which everything in the world is composed. This stuff he calls ‘pure experience’. Knowing, he says, is a particular sort of relation between two portions of pure experience. The subject-object relation is derivative: ‘experience, I believe, has no such inner duplicity’.

Bertrand Russell, History of Western Philosop…, loc. 2895